All solution-processed ITO free flexible organic light-emitting diodes

Abstract

Roll-to-roll (R2R) printing and coating techniques can be used for low cost and large-area mass production of organic electronic devices. While research in the photovoltaic field has developed R2R printed large-scale solar modules, research in solution-processed OLEDs has not progressed as far yet. In this work, we investigate all-solution processed OLEDs based on ink-jet printed silver bottom electrodes and spin-coating of all other layers. Ink-jet printing provides the advantages of mask-free patterning and non-contact manufacturing. As the top electrode, a conductive PEDOT:PSS formulation easily processable on organic layers due to a low contact angle is utilized. The all-solution processed top-emitting OLEDs achieve high luminance (7 000 cd m⁻²) and an efficiency close to that of reference devices with evaporated electrodes: 4.2 cd A⁻¹vs. 7.6 cd A⁻¹, respectively. The shelf stability is also tested and after seven months, the all solution-processed encapsulated OLED retains 82% of its initial EQE.